c-myb and Mml 1,2 and 3 continue to be the focus of the laboratory since we have found that these loci are important to the development of promonocytic leukemia. These are targets of insertional mutagenesis by retroviruses in our animal model. In addition, this year we have found new proviral insertion sites called Mml4 and 5.Our laboratory has shown that the c-myb oncogene, which encodes a transcription factor, can be activated in promonocytic leukemias when the retrovirus integrates into the locus. Previously, we characterized the many ways this gene can be activated by retroviral insertion and the mechanistic consequences of this integration. Recently, a major goal has been to characterize the functional role of this transcription factor in leukemic cells. In particular, we are interested in identifying target genes regulated by this transcription factor that are involved in proliferation and anti- apoptotic processess. This year we have continued studies which have show that c-myc is an important target through which the c-Myb protein exerts its positive effect on proliferation. Using both a Myb-estrogen receptor fusion protein and a dominant negative Myb-estrogen receptor protein, both of which can be induced rapidly by tamoxifen, we have demonstrated that c-Myb regulates c-myc at the transcriptional level. These data were confirmed using conditional induction of c-myb gene transcription via a vector with a metallothionein promoter. Our studies on targets are being extended in two ways. First, we are looking for new target genes of c-Myb using microarray technology and second, we are looking for genes that are regulated by a related gene B-Myb. Candidate targets have already been identified. We discovered that the loci Mml1,Mml2 and Mml3 are individually associated with the development of a subset of acute monocytic leukemias and all three map to the same region on chromosome 10. Although they are connected on the same BAC clone they are separated from each other by greater than 20 kb. Presently, a major focus of the laboratory is the characterization of transcripts from these loci that may encode a new proto-oncogene or tumor suppressor gene. Greater than 60 kb of this region have been sequenced resulting in the finding of several homologous ESTs which have been useful in the identification of genes encoded by this region. We are presently determining if any of these genes is altered in its transcription due to integration of proviruses in general region. In addition, we identifed through the use of retroviral insertional mutagenesis, two other apparently novel loci Mml4 and Mml5 that are located on chromosomes other than chromosome 10. On of this has been mapped to chromosome 13. - animal model, c-myb, Insertional Mutagenesis, Leukemia, proteolysis, retrovirus, - Neither Human Subjects nor Human Tissues